The biotech company (NASDAQ: SGEN) and its partner, Cambridge, MA-based Millennium: The Takeda Oncology Company, are presenting results today from a study of 58 patients who got the targeted drug for a rare and deadly malignancy called anaplastic large cell lymphoma (ALCL). More than half of the patients (53 percent) had their tumors completely eradicated after getting dosed with brentuximab vedotin, and a total of 86 percent had their tumors shrink by half or more, according to findings being presented today at the American Society of Hematology (ASH) meeting in Orlando, FL.

The most common severe side effect, in one-fifth of patients, was neutropenia, in which infection-fighting white blood cells get knocked out. Doctors don’t know how long the remissions are lasting, because more than half of patients are still in remission after six months of follow-up.

“Nearly all patients in this trial had reductions in tumor volume, including a remarkable rate of complete remissions,” said Dr. Andrei Shustov, a hematologist at the University of Washington, in a Seattle Genetics statement. Another researcher, Pier Zinzani of Seràgnoli University of Bologna, Italy, noted that since this drug was given by itself, with no other chemotherapy combinations, it was particularly impressive. “Single-agent activity of this magnitude is rarely seen in oncology,” he said in a statement.

This is the second important batch of clinical trial results for this drug at this year’s hematology meeting. On Sunday, researchers reported that the new drug generated complete remissions in about one-third of patients with Hodgkin’s disease, and shrank tumors by half or more in another 40 percent of patients. Those results, combined with the new findings among patients with the related malignancy known as ALCL, have given Seattle Genetics the confidence to seek FDA approval before the end of March for brentuximab vedotin for both forms of cancer. If approved, it will be the first marketable product for Seattle Genetics, and it will be the only drug available that combines the specific tumor-targeting capability of an antibody with an extra-potent dose of a toxin to give it extra tumor-killing kick.

Seattle Genetics CEO Clay Siegall

Investors have been hotly anticipating this data set ever since Seattle Genetics offered a basic preview press release on the trials, back in September and October. Since investors already bid up Seattle Genetics shares more than 56 percent heading into the weekend’s detailed data dump, there was a sell-on-the-news reaction yesterday, in which the stock dropped about 4 percent.

“Overall, we believe the results are very good, and that this drug is exceedingly likely to be approved in the second half of 2011,” said Cory Kasimov, an analyst with JP Morgan, in a note to clients after the Hodgkin’s data was reported on Sunday. “However, considering that prevailing expectations were already quite high, we suspect it will be difficult for this weekend’s update to trigger near-term upside in Seattle Genetics shares.”

Here’s what the latest study showed of the new drug. The 58 patients who enrolled had relapsed or treatment-resistant forms of … Next Page »